It has been officially estimated that between the years 1492 and 1894 the world’s production of gold equaled about $8,000,000,000. Of this amount a little less than $4,000,000,000 was held as gold reserve in 1894, the remainder having been lost or absorbed in the arts or in the manufacture of jewelry. Since 1894 the consumption of gold in the arts has been between $50,000,000 and $100,000,000 annually, or for the 27 years about $2,100,000,000 out of a total production of $9,000,000,000—almost 25 per cent.[158]
[158] Jennings, Hennen: “The Gold Industry and Gold Standard,” 1919.
GEOLOGICAL OCCURRENCE
Gold is widely distributed, both geographically and geologically. It is found in about 60 countries in all parts of the world and occurs in rocks of all ages, from Archean to Quaternary, often in association with other metals, as silver, copper, tellurium, lead, and iron.
Gold deposits may be broadly classified as lodes and placers. Lode deposits are also known as vein or quartz deposits; and in them the gold is found with silica or quartz in irregular masses, strings, scales, plates, and crystals, or more often in microscopic particles in the sulphide minerals or the gangue. Much the same methods are used for extracting the ore as are used in mining silver, lead, or zinc.
Placer or alluvial deposits are sedimentary beds of gravel or sand in which the particles of gold, washed from the mother lode, have been concentrated by the action of water. Most of the placer deposits lie in the open, along the bed of a river, but some are covered by a sheet of lava or other non-productive rock. The gold occurs as scales, grains, slugs or nuggets. A number of large nuggets have been found, the largest being the Australian “Welcome Stranger,” weighing 2,520 ounces and valued at about $42,000. Usually, however, the particles of gold are minute.
Placer deposits are worked by one of the following methods, depending on the nature and richness of the alluvium: sluice mining, hydraulic mining, dredging, or drift mining.
During the early years of what has been called the modern era of gold mining, beginning with the discovery of gold in California in 1848, most of the world’s annual production came from placer deposits. De Launay estimates that from 1848 to 1875 placers contributed 87 per cent. In more recent years, with the exhaustion of the easily discovered and the easily worked placer mines, the proportion has decreased and at present it is probably not more than 10 per cent. Today the great gold mines of the world are lode mines. The world’s deepest gold mine has attained a vertical depth of 5,900 feet.
After making all allowances for further discoveries, students of the subject are of the opinion that the world’s gold production has already reached its zenith and that a decline may be expected.[159]
[159] The above discussion of the geological occurrence of gold is based mainly on “The Gold Industry and Gold Standard” and other articles by Hennen Jennings, consulting engineer, U. S. Bureau of Mines.